1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, more particularly to an electrophotographic photosensitive member containing a disazo pigment having a specific molecular structure in the photosensitive layer.
2. Related Background Art
In the prior art, as the electrophotographic photosensitive member by use of an inorganic photoconductive substance, those using selenium, cadmium sulfide, zinc oxide, etc. have been widely known.
On the other hand, as the electrophotographic photosensitive member by use of an organic photoconductive substance, those using a photoconductive polymer as represented by poly-N-vinylcarbazole or a low molecular weight organic photoconductive substance such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole and further a combination of such organic photoconductive substance with various dyes or pigments have been known.
The electrophotographic photosensitive member by use of an organic photoconductive substance has such advantages that film forming property is good, and that it can be produced by coating with extremely high productivity to provide photosensitive members at low cost. Also, it has the advantage that by selection of the sensitizer to be used such as dye or pigment, color sensitivity can be controlled freely, and has been heretofore widely investigated. Particularly, in recent years, by development of the function separation type photosensitive member comprising a layer containing an organic photoconductive pigment as the charge generation layer and a layer containing a photoconductive polymer or a low molecular weight organic photoconductive substance as mentioned above as the charge transport layer laminated on one another, remarkable improvements have been done to sensitivity and durability which have been the drawbacks of the organic electrophotographic photosensitive member of the prior art, to make it possible to provide the photosensitive member for practical application.
As the disazo pigment to be used in this kind of photosensitive member, for example, dicyanofluorenylidene type disazo pigments as disclosed in Japanese Laid-open Patent Publication No. 58-194035 benzanthrone type disazo pigments as disclosed in Japanese Laid-open Patent Publication No. 61-219048 have been known. However, the photosensitive member by use of these disazo pigments proved to be not satisfactory with respect to sensitivity and potential stability when used repeatedly.